1. Field of the Invention
The present invention relates to a toner for electrophotography to be preferably used for an electrophotographic method performing flash fixing, an electrostatic recording method, a magnetic recording method, or the like, and a developer for electrophotography using the same, a process cartridge using the same, an apparatus for forming an image using the same, and a method for forming an image using the same.
2. Description of the Related Art
In general, for image forming in an electrophotographic system, the following processes are employed: (1) charging a photoconductor electrostatically; (2) exposing the photoconductor to light (formation of a latent image); (3) developing the latent image by a toner; (4) transferring the toner onto a transfer material; (5) fixing the toner onto the transfer material; and other processes. Examples of a method of fixing the toner transferred onto the transfer material may include: a method in which the toner is fused by application of pressure or heat, or by a combination thereof, then solidified and fixed; and a method in which the toner is fused by irradiation with a light energy, then solidified and fixed. Recently, out of these methods, attention has been focused on oven fixing, flash fixing utilizing a flash light, or the like, which will not be detrimentally affected through an application of pressure or heat, from the viewpoint that the method is capable of forming a fine, high-resolution image.
Namely, in these fixing methods, the toner is not required pressure for fixation. This eliminates the problem of offset, or the like, which arises in the case of a fixing roller, or the like. In consequence, these methods advantageously cause less degradation in image resolution (reproducibility) in the fixing step. Further, the toner is not required to be heated by means of a heat source or the like. This eliminates the problem that printing cannot be performed until the heat source (a fixing roller, or the like) will be preheated to a desired temperature upon power-on, or other problems. In consequence, these methods also have an advantage in that printing is possible immediately after power-on. Still further, these methods do not require a high-temperature heat source, and hence are advantageously capable of properly avoiding the temperature rising in the apparatus, or the like. Particularly, the flash fixing method also has the following advantages: even if recording paper is jammed in a fixing unit due to a system malfunction, or in other cases, the recording paper will not burn due to the heat from the heat source; and other advantages.
In general, a color toner has a low light absorption efficiency, resulting in a lower fixability as compared with a black toner. For this reason, a large number of technologies for improving the fixability by adding an infrared absorbent to the toner are proposed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 60-63545, 60-63546, 60-57858, 60-57857, 58-102248, 58-102247, 60-131544, 60-133460, and 61-132959, WO 99/13382, JP-A Nos. 2000-147824, 07-191492, 2000-155439, 06-348056, 10-39535, 2000-35689, 11-38666, 11-125930, 11-125928, 11-125929, and 11-65167.
In these cases, however, it is not possible to achieve the compatibility between the fixability and the void resistance in the toner. Herein, the term “void” denotes an image defect uniquely occurring upon performing flash fixing, and a phenomenon that a printed part is left out. The void is caused due to the following reasons. For example, the outermost surface temperature of the toner is increased up to about 500° C. during flash fixing. Accordingly, the toner is fused, so that the air mixed in the toner expands all at once. As a result, the toner is blown off. Moreover, toner particles flocculate upon fusing due to the surface tension of the toner particles. Although the toner viscosity upon fusing is desired to be high in order to prevent the occurrence of the void, a toner having a low toner viscosity is desired for improving the fixability. Therefore, it is difficult to ensure the high-level compatibility between the fixability and the void resistance.
Incidentally, technologies of allowing waxes to be contained in a toner are commonly used in image forming by a heat roll fixing method, and the like. The technologies are disclosed in, for example, Japanese Patent Application Publication (JP-B) Nos. 52-3304, 52-3305, and 57-52574. In these technologies, the waxes are used for improving the offset resistance of the toner for heat roll for example, in Japanese Patent Application Publication (JP-B) No. 52-3305, JP-A Nos. 58-215659, 62-100775, 04-124676, 04-299357, 04-362953, 05-197192, and 08-334919, and the like, there is disclosed a toner containing two or more waxes for the purpose of producing more effects of wax addition over a low-temperature region to a high-temperature region.
However, even if these technologies are directly applied to flash toner as they are, it is not possible to obtain sufficient effects. In the flash fixing system, it has been unable to obtain a toner whose fixability and void resistance have both been implemented at a high level.